For several decades now, the mechanized cutting of vegetation has been habitually performed by machines or appliances powered by electricity or fuel, in which one or more metal or synthetic blades, or synthetic cords, or indeed any other cutting member capable of cutting the vegetation encountered in its path, is propelled at high speed. These machines or appliances include in particular lawnmowers on the one hand, and grass trimmers and edge trimmers on the other, the latter appliances having a rotary head driven at high speed and turning one or more synthetic cords.
With this type of machine or appliance, it is the violent impact (due to the speed of rotation generated by the motor) of more or less sharp objects, such as the blades of lawnmowers or the cords of trimmers, on the vegetation that performs the cutting work by a "smashing" action: a nonmoving lawnmower blade or trimmer cord has no cutting power in itself, and only the fact that these parts are spun at high speed can cut vegetation. Hence, in order to function effectively, existing machines and appliances are usually polluting and noisy and consume electricity or fuel and oil in order to produce the necessary motive force.
In the case of grass and edge trimmers, attempts have already been made to reduce the noise by giving the cutting cord special configurations, such as twisted or undulating shapes. However, this only partly solves the problem because the noise of the motor itself is of course not suppressed, and moreover pollution is not reduced.
It is against this background that a number of standards are currently being set up in order to reduce all forms of pollution (noise, chemical, etc.) generated by machines and appliances for the upkeep of vegetation.
Besides the conventional solutions cited above, proposals have been made for systems that cut vegetation with jets of water. Examples that may be cited here are documents DE-A-3135927, DE-U-9300077, GB-A-2093327 and FR-A-2312953.
All these documents utilize the principle of "fixed" cutting jets which are only moved past the vegetation to be cut by the forward motion of the appliance on which the jet emitting means are supported, the speed of the jets relative to the vegetation to be cut thus remaining very small. These systems retain a number of disadvantages in particular:
A fixed or virtually fixed jet is liable simply to press the vegetation which it encounters down on the ground without cutting it, especially in the case of fine vegetation such as grass. PA1 In order to "sweep" a certain width of ground, known systems use a larger number of jets, arranging them one behind the other; this means that separating fingers must be positioned opposite the jet ejecting nozzles in such a way as to direct the vegetation toward the jets. PA1 Most systems proposed to date include means for collecting and recycling the ejected water. This complicates the structure and prevents the water from being used to irrigate or treat the vegetation and/or soil. PA1 Lastly, these known systems are based on replacing a conventional bladed lawnmower with an appliance using transverse jets of water; none of these systems are designed as lightweight--that is, specifically, portable--appliances comparable with modern grass or edge trimmers. PA1 means for supplying water at pressure, PA1 means for ejecting the water at pressure in the form of at least one jet of water and directing it at the vegetation to be cut, and PA1 means for causing movement of the jet or jets of water.